Bone fractures disrupt essential metabolic and mechanical functions of the skeleton and thus threaten health and quality of life. Fracture healing attempts to restore the shape, function, and material properties of bone. Biomineralization is thought to proceed through a sequence of transient phases before reaching a stable form, a progression that has been observed in vitro for invertebrates and dentin and recently was discovered in vivo for fetal murine tissue by the Morris group. However, the biochemical mechanisms behind bone tissue mineralization, particularly during fracture healing, are still not well understood. While fracture callus mineralization is thought to be similar to growth plate mineralization, the occurrence of transient mineral phases during fracture repair have not been examined in real time. The hypotheses for this study are that (1) fracture healing includes a mineral transformation from a disordered phase through a transient phase to a final stable phase, and this mechanism is similar regardless of skeletal age and stage of development;and (2) biochemical composition of the fracture callus can be monitored noninvasively throughout the healing process, and these measurements are predictive of callus material quality. To test the hypotheses, mineralization kinetics will be followed for the fracture callus at the femoral middiaphysis of male wild type mice. Raman spectroscopy will examine the kinetics over a 24-hour period in the early stages of fracture repair for mice of different ages. Next, bone matrix and mineral properties will be studied in the fracture callus throughout healing in skeletally mature male wild type mice. The biochemical properties observed by noninvasive Raman spectroscopy will be correlated with geometric and mechanical properties to assess the ability of this technique to characterize the fracture callus integrity. The proposed study will provide unique information about the progression of tissue mineralization during fracture healing and will assess the ability of a noninvasive Raman spectroscopic system to monitor the healing process. Overall, the goals of these experiments are to gain insights into the mechanisms of fracture healing mineralization and to provide a clinical imaging and analysis tool to assess the fracture site noninvasively, regardless of age. This type of information could be invaluable in the detection and correction of abnormal healing and thus may be useful for developing strategies to promote successful bone repair.